Historically, propeller blades have been made with different materials and architectures. Both concepts have evolved from wooden blades to composite materials with an increasing complexity in their configurations.
As is known, blades are mounted on propellers, which are located close to the aircraft structure, vital systems for the aircraft proper operation, and also close to the opposite propeller. In addition to their compromised location, blades in propeller engines are not covered by a fairing or nacelle. Both conditions, being in a potentially risky location for an aircraft normal operation and being unprotected, mean that blade impacts have been recently considered by airworthiness authorities.
Blades may break, in part or completely, or be entirely released from the propeller hub. In almost all these cases, this leads to serious damages in the aircraft structure and/or its systems because of the impact, and to a consequent unbalanced situation of the engine caused by the broken or released blade.
Therefore, airworthiness authorities have requested aircraft manufacturers and engine suppliers to consider the impact scenario due to a blade release, in order to be able to withstand the impact, especially when the aircraft is in flight. Thus, the risk of catastrophic effects derived from the release has to be minimized.
It would therefore be desirable to provide a propeller that complies with airworthiness requirements to ensure a continued safe flight and landing of an aircraft in which a blade has been partially or entirely released.